Power supply arrangement for multi-stage amplifier

ABSTRACT

There is disclosed a multi-stage amplifier comprising: a first amplifier stage; a second amplifier stage; a first voltage supply stage arranged to provide a supply voltage to the first amplifier in dependence on an average power of a signal to be amplified; and a second voltage supply stage arranged to provide a supply voltage to the second amplifier in dependence on an instantaneous power of a signal to be amplified.

CROSS-REFERENCE TO RELATED APPLICATION(S)

U.S. patent application Ser. No. 14/186,265, with a filing date of Feb.21, 2014 and British patent application GB 0821077.5, with a filing dateof Nov. 18, 2008, are incorporated herein by reference.

BACKGROUND TO THE INVENTION

1. Field of the Invention

The present invention relates to power supply arrangements formulti-stage amplifiers. The invention is particularly but notexclusively concerned with power supply arrangements for multi-stageamplifiers which utilise envelope tracking techniques.

2. Description of the Related Art

In a multi-stage amplifier arrangement, a plurality of amplifier stagesare provided in series for amplification of a signal. An examplemulti-stage amplifier arrangement for amplification of a radio frequency(RF) signal may comprise a driver amplifier stage followed by a poweramplifier stage. Such a two-stage amplifier arrangement is typicallyprovided in a transmitter in a handset or mobile device of a mobilecommunications system.

In order to achieve efficiency in the operation of power amplifierarrangements, various schemes have been disclosed in the prior art forefficiently providing a supply voltage to an amplifier stage, andparticularly to a power amplifier stage. A particularly advantageoushigh efficiency amplification scheme is disclosed in European Patent No.1597821 in the name of Nujira Limited.

In multi-stage amplifier arrangements, it is known in the prior art toapply a modulated supply voltage simultaneously to two or moreamplification stages. Such an approach is successful for theamplification of narrowband signals, such as GSM/EDGE 200 kHz bandwidthsignals.

However the envelope tracking principles of a high efficiency trackingsupply place tight limits on time alignment between the various signalpaths in the system. For narrowband signals, these limitations can behandled. However for wideband signals, such as in wideband code divisionmultiple access (WCDMA) systems, world interoperability for microwaveaccess (WiMAX) systems, or long term evolution (LTE) systems forexample, these requirements create difficulties in providing supplymodulation on more than one amplifier stage at any given time.

In the prior art, therefore, for a multi-stage amplifier arrangementwhere a highly efficient modulated power supply stage is provided usingenvelope tracking, typically such supply modulation is provided for onlyone amplifier stage. The one or more remaining amplifier stages arearranged to operate from fixed supply voltages. The operation of the oneor more remaining amplifier stages based on fixed supply voltagesresults in poor operating efficiency. This poor efficiency isparticularly relevant for systems where the RF output can vary over alarge dynamic range, and/or the RF signal has a high peak-to-averagepower ratio (PAPR).

It is an object of the invention to provide a multi-stage amplifierarrangement in which efficiency of performance is improved.

SUMMARY OF THE INVENTION

In one aspect the invention provides a multi-stage amplifier comprising:a first amplifier stage; a second amplifier stage; a first voltagesupply stage arranged to provide a supply voltage to the first amplifierin dependence on an average power of a signal to be amplified; and asecond voltage supply stage arranged to provide a supply voltage to thesecond amplifier in dependence on an instantaneous power of a signal tobe amplified.

The first voltage supply stage may comprise a switched supply stage. Theswitched supply stage may select one of a plurality of supply voltagesgenerated in the second voltage supply stage. The switched supply stagemay select one of a plurality of supply voltages generated in the firstvoltage supply stage. The multi-stage amplifier may further comprisemeans for determining the instantaneous power and the average power,wherein the average power is determined over a predetermined timeinterval.

There may be provided a means for determining the average of the supplygenerated by the second supply voltage stage, and providing the firstsupply voltage in dependence upon the determined average. The means fordetermining the average of the supply generated by the second supplyvoltage stage may comprise a low pass filter. The first voltage supplystage may further comprise a switched supply stage, wherein the switchedsupply is controlled by the determined average. The multi-stageamplifier may further comprise a sample-and-hold stage for sampling thedetermined average.

The first and second voltage supply stages may be arranged toselectively provide supply voltages to the first and second amplifierstages, wherein in a first mode of operation a signal is amplified bythe first and second amplifier stages, and the first supply voltagestage is selected to provide a supply voltage to the first amplifierstage and the second supply voltage stage is selected to provide asupply voltage to the second amplifier stage, and in a second mode ofoperation the second amplifier is bypassed, the signal being amplifiedby the first amplifier stage, and the second supply voltage stage beingselected to provide a supply voltage to the first amplifier stage.

In one aspect the invention provides a multi-stage amplifier comprising:a first amplifier stage; a second amplifier stage; a first trackingpower supply stage for providing a tracking supply voltage to the firstamplifier; and a second tracking power supply stage, for providing atracking supply voltage to the second amplifier, wherein the secondtracking power supply voltage tracks faster than the first.

In one aspect the invention provides a method of amplifying a signal inan amplification stage comprising a first amplifier stage; a secondamplifier stage; a first voltage supply stage; and a second voltagesupply stage, the method comprising: arranging the first voltage supplystage to provide a supply voltage to the first amplifier in dependenceon an average power of a signal to be amplified; and arranging thesecond voltage supply stage to provide a supply voltage to the secondamplifier in dependence on an instantaneous power of the signal to beamplified.

The first voltage supply stage may comprise a switched supply stage. Theswitched supply stage may select one of a plurality of supply voltagesgenerated in the second voltage supply stage. The switched supply stagemay select one of a plurality of supply voltages generated in the firstvoltage supply stage.

The method may further comprise determining the average of the supplygenerated by the second supply voltage stage, and providing the firstsupply voltage in dependence upon the determined average.

The step of determining the average of the supply generated by thesecond supply voltage stage may comprise low pass filtering.

The first voltage supply stage may further comprise a switched supplystage, wherein the method further comprises controlling the switchedsupply by the determined average.

The method may further comprise a sampling the determined average.

The first and second voltage supply stages may selectively providesupply voltages to the first and second amplifier stages, wherein in afirst mode of operation a signal is amplified by the first and secondamplifier stages, and the first supply voltage stage is selected toprovide a supply voltage to the first amplifier stage and the secondsupply voltage stage is selected to provide a supply voltage to thesecond amplifier stage, and in a second mode of operation the secondamplifier is bypassed, the signal being amplified by the first amplifierstage, and the second supply voltage stage being selected to provide asupply voltage to the first amplifier stage.

In one aspect the invention provides a method of amplifying a signal inan amplification stage comprising a first amplifier stage; a secondamplifier stage; a first voltage supply stage; and a second voltagesupply stage, the method comprising: arranging the first voltage supplystage to provide a tracking supply voltage to the first amplifier; andarranging the second voltage supply stage to provide a tracking supplyvoltage to the first amplifier, wherein the second voltage supply stagetracks faster than the first.

In one aspect the invention provides a multi-stage amplifier including afirst amplifier stage, a second amplifier stage, and a tracking voltagesupply stage arranged to provide a supply voltage in dependence on aninstantaneous power requirement, wherein in a first mode of operation asignal is amplified by the first and second amplifier stages, and thesupply voltage to the second amplifier stage is provided by the trackingvoltage supply, and in a second mode of operation the second amplifierstage is bypassed, the signal being amplified by the first amplifierstage, and the supply voltage to the first amplifier stage is providedby the tracking voltage supply.

The multi-stage amplifier according may further comprise a furthervoltage supply stage arranged to provide a supply voltage in dependenceon an average power requirement, wherein in the first mode of operationthe further voltage supply stage provides a supply voltage for the firstamplifier stage.

The first voltage supply stage may comprise a switched supply stage.

The switched supply stage may select one of a plurality of supplyvoltages generated in the second voltage supply stage. The switchedsupply stage may select one of a plurality of supply voltages generatedin the first voltage supply stage.

There may be provided a means for determining the average of the supplygenerated by the second supply voltage stage, and providing the firstsupply voltage in dependence upon the determined average.

The means for determining the average of the supply generated by thesecond supply voltage stage may comprise a low pass filter.

The first voltage supply stage may further comprises a switched supplystage, wherein the switched supply is controlled by the determinedaverage.

The multi-stage amplifier may further comprise a sample-and-hold stagefor sampling the determined average.

The first voltage supply stage may generate the supply voltage independence on an average power requirement of the signal to be amplifiedby the first amplifier; and the second voltage supply stage generatesthe supply voltage in dependence on an instantaneous power requirementof the signal to be amplified by the second amplifier.

In one aspect the invention provides a multi-stage amplifier including afirst amplifier stage, and a tracking voltage supply stage whichfast-tracks a signal to be amplified, wherein in a first mode ofoperation a signal is amplified by the first and second amplifierstages, and the supply voltage to the second amplifier stage is providedby the tracking voltage supply, and in a second mode of operation thesecond amplifier stage is bypassed, the signal being amplified by thefirst amplifier stage, and the supply voltage to the first amplifierstage is provided by the tracking voltage supply.

The multi-stage amplifier may further comprise a further trackingvoltage supply stage which slow-tracks the signal to be amplified,wherein in the first mode of operation the further voltage supply stageprovides a supply voltage for the first amplifier stage.

In one aspect the invention provides a method of amplifying a signal ina multi-stage amplifier including a first amplifier stage, a secondamplifier stage, and a tracking voltage supply stage arranged to trackin dependence on an instantaneous power, the method comprising: in afirst mode of operation a signal is controlled to be amplified by thefirst and second amplifier stages, and the supply voltage to the secondamplifier stage is provided by the tracking voltage supply, and in asecond mode of operation the second amplifier stage is bypassed, thesignal being amplified by the first amplifier stage, and the supplyvoltage to the first amplifier stage is provided by the tracking voltagesupply.

The method may further comprise providing a further voltage supply stagearranged to track in dependence on an average power, wherein in thefirst mode of operation the further voltage supply stage provides asupply voltage for the first amplifier stage.

In one aspect the invention provides a method of amplifying a signal ina multi-stage amplifier including a first amplifier stage, a secondamplifier stage, and a tracking voltage supply stage adapted tofast-track a signal to be amplified, the method comprising: in a firstmode of operation a signal is controlled to be amplified by the firstand second amplifier stages, and the supply voltage to the secondamplifier stage is provided by the tracking voltage supply, and in asecond mode of operation the second amplifier stage is bypassed, thesignal being amplified by the first amplifier stage, and the supplyvoltage to the first amplifier stage is provided by the tracking voltagesupply.

The method may further comprise a further tracking voltage supply stageadapted to slow-track the signal to be amplified, wherein in the firstmode of operation the further voltage supply stage provides a supplyvoltage for the first amplifier stage.

In one aspect the invention provides a multi-stage amplifier including afirst amplifier, an average tracking voltage supply stage which tracksthe average power of a signal to be amplified, and an instantaneoustracking voltage supply stage which tracks the instantaneous power of asignal to be amplified, wherein the power supply for the power amplifieris selectively provided by either the average tracking voltage supply orthe instantaneous tracking voltage supply.

There may be provided a second amplifier arranged in series to receiveat it's input the output of the first amplifier, wherein in a first modeof operation the power supply for the first amplifier may be provided bythe average tracking voltage supply, and the power supply for the secondamplifier is provided by the instantaneous tracking voltage supply, andin a second mode of operation the power supply for the first amplifiermay be provided by the instantaneous tracking voltage supply and thesecond amplifier is bypassed.

In a third mode of operation the power supply for the first amplifiermay be provided by the average tracking voltage supply and the secondamplifier is bypassed.

The average tracking voltage supply may be provided by a switched supplystage, and the instantaneous tracking voltage supply is provided by anerror correction stage in dependence on the average tracking voltagesupply. The average tracking voltage may provided by a filtering meansarranged to filter the instantaneous tracking voltage.

There may be provided a second amplifier arranged in parallel with thefirst amplifier, the first and second amplifiers having a common inputand a common output, wherein in a first mode of operation the firstamplifier is selected and the second amplifier is disabled, the powersupply to the first amplify being provided by the average trackingvoltage supply, and in the second mode of operation the second amplifieris selected and the first amplifier is disabled, the power supply to thesecond amplified being provided by the instantaneous tracking voltagesupply.

There may be provided a third amplifier arranged to provide an input tothe first and second amplifiers, wherein in the first or second mode ofoperation the power supply for the third amplifier is provided by theaverage tracking voltage supply, and in a third mode of operation thepower supply for the third amplifier is provided by the instantaneoustracking voltage supply and the first and second amplifiers arebypassed.

The average tracking voltage supply may be provided by a switched supplystage, and the instantaneous tracking voltage supply is provided by anerror correction stage in dependence on the average tracking voltagesupply. The average tracking voltage may be provided by a filteringmeans arranged to filter the instantaneous tracking voltage.

There may be provided a second amplifier arranged in parallel with thefirst amplifier, the first and second amplifiers having a common inputand a common output, wherein in a first mode of operation the first andsecond amplifiers are both enabled, the power supply to the first andsecond amplifiers being provided by the instantaneous tracking voltagesupply.

In a second mode of operation one amplifier may be enabled and the otheramplifier may be disabled, the power supply to the selected amplifierbeing provided by the instantaneous tracking voltage supply.

In a second mode of operation one amplifier may be enabled and the otheramplifier may be disabled, the power supply to the selected amplifierbeing provided by the average tracking voltage supply.

The first and second amplifiers may comprise a Doherty configuration.

The average tracking voltage supply may be provided by a switched supplystage, and the instantaneous tracking voltage supply is provided by anerror correction stage in dependence on the average tracking voltagesupply.

The average tracking voltage may be provided by a filtering meansarranged to filter the instantaneous tracking voltage.

In one aspect the invention provides a method of amplifying a signal ina multi-stage amplifier including a first amplifier, comprising trackingthe average power of a signal to be amplified, tracking theinstantaneous power of a signal to be amplified, and selectivelyproviding a power supply to the amplifier from either the averagetracked voltage or the instantaneous tracked voltage.

The method may provide a second amplifier arranged in series to receiveat it's input the output of the first amplifier, wherein in a first modeof operation the power supply for the first amplifier is provided by theaverage tracking voltage supply, and the power supply for the secondamplifier is provided by the instantaneous tracking voltage supply, andin a second mode of operation the power supply for the first amplifieris provided by the instantaneous tracking voltage supply and the secondamplifier is bypassed.

The method may provide in a third mode of operation the power supply forthe first amplifier by the average tracking voltage supply and thesecond amplifier is bypassed.

The method may provide that the average tracking voltage supply isprovided by a switched supply stage, and the instantaneous trackingvoltage supply is provided by an error correction stage in dependence onthe average tracking voltage supply.

The method may provide that the average tracking voltage is provided bya filtering means arranged to filter the instantaneous tracking voltage.

The method may provide that a second amplifier is arranged in parallelwith the first amplifier, the first and second amplifiers having acommon input and a common output, wherein in a first mode of operationthe first amplifier is selected and the second amplifier is disabled,the power supply to the first amplify being provided by the averagetracking voltage supply, and in the second mode of operation the secondamplifier is selected and the first amplifier is disabled, the powersupply to the second amplified being provided by the instantaneoustracking voltage supply.

The method may provide a third amplifier arranged to provide an input tothe first and second amplifiers, wherein in the first or second mode ofoperation the power supply for the third amplifier is provided by theaverage tracking voltage supply, and in a third mode of operation thepower supply for the third amplifier is provided by the instantaneoustracking voltage supply and the first and second amplifiers arebypassed.

The method may provide that the average tracking voltage supply isprovided by a switched supply stage, and the instantaneous trackingvoltage supply is provided by an error correction stage in dependence onthe average tracking voltage supply.

The method may provide that the average tracking voltage is provided bya filtering means arranged to filter the instantaneous tracking voltage.

The method may provide that a second amplifier is arranged in parallelwith the first amplifier, the first and second amplifiers having acommon input and a common output, wherein in a first mode of operationthe first and second amplifiers are both enabled, the power supply tothe first and second amplifiers being provided by the instantaneoustracking voltage supply.

The method may provide that in a second mode of operation one amplifieris enabled and the other amplifier is disabled, the power supply to theselected amplifier being provided by the instantaneous tracking voltagesupply.

The method may provide in a second mode of operation one amplifier isenabled and the other amplifier is disabled, the power supply to theselected amplifier being provided by the average tracking voltagesupply.

The method may provide that the first and second amplifiers comprise aDoherty configuration.

The method may provide that the average tracking voltage supply isprovided by a switched supply stage, and the instantaneous trackingvoltage supply is provided by an error correction stage in dependence onthe average tracking voltage supply.

The method may provide that the average tracking voltage is provided bya filtering means arranged to filter the instantaneous tracking voltage.

BRIEF DESCRIPTION OF THE FIGURES

The invention will now be described by way of example with reference tothe accompanying Figures, in which:

FIG. 1 illustrates the principles of an efficient multi-stage amplifierarrangement in accordance with an inventive arrangement;

FIG. 2 illustrates an embodiment of the inventive arrangement of FIG. 1;

FIG. 3 illustrates a second embodiment of the inventive arrangement ofFIG. 1;

FIG. 4 illustrates a third embodiment of the inventive arrangement ofFIG. 1;

FIG. 5 illustrates a fourth embodiment of the inventive arrangement ofFIG. 1;

FIG. 6 illustrates the principles of an efficient multi-stage amplifierarrangement in accordance with an inventive arrangement;

FIG. 7 illustrates an embodiment of the inventive arrangement of FIG. 6;and

FIG. 8 illustrates a further embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention is described herein with reference to particularembodiments and exemplary arrangements. The invention is not, however,limited to the specifics of such arrangements described. In particularthe invention is described in the context of a multi-stage amplifierarrangement comprising a driver amplifier stage and a power amplifierstage, for the amplification of an RF signal. It should be understood byone skilled in the art that the invention is not limited to amulti-stage amplifier arrangement including only two amplifier stages,and the principles of the invention apply to any multi-stage amplifierarrangement including two or more amplifier stages. Further one skilledin the art will appreciate that the principles of the inventivearrangement and the embodiments described herein are not limited to theamplification of RF signals.

The invention is also described herein, in embodiments, in the contextof a high efficiency envelope tracking modulated power supply stage forproviding a power supply for an amplifier stage, particularly the poweramplifier stage. One skilled in the art will appreciate that theinvention is not limited to a particular type of efficient modulatedpower supply stage. A particularly efficient modulated power supplystage is disclosed in European Patent No. 1597821, and the use of suchan efficient power supply stage in combination with embodiments of theinvention described herein provides a particularly beneficialarrangement. However the invention is not limited to the use of such aspecific modulated power supply arrangement, and the principles of theinvention and its embodiments as described herein may be utilised incombination with any advantageous tracking or modulated power supplyarrangement.

With reference to FIG. 1 there is illustrated a multi-stage amplifierarrangement denoted by reference numeral 100, including a firstamplifier stage being a driver stage 106, and a second amplifier stagebeing a power amplifier stage 108. An RF signal to be amplified isreceived from an RF source on line 114, and provides an input to thedriver stage 106. The output of the driver stage 106 is provided on line116, and forms an input to the power amplifier stage 108. The poweramplified RF signal is provided on line 118 at the output of the poweramplifier stage 108 as the RF output. As illustrated in FIG. 1, each ofthe amplifier stages is associated with a respective voltage supplystage. Thus a voltage supply stage 102 is arranged to provide the supplyvoltage for the driver stage 106, and a voltage supply stage 104 isarranged to provide the supply voltage for the power amplifier stage108. Each of the voltage supply stages 102 and 104 receives a batteryvoltage on a line 110, and a reference signal on a line 112. Each of thevoltage supply stages 102 and 104 provide a supply voltage to therespective amplifier stages 106 and 108 in dependence upon the batteryvoltage and the reference signal.

The voltage supply stage 104 is preferably an envelope trackingmodulated power supply stage, which provides fast tracking of the supplyvoltage delivered to the power amplifier stage 108. The reference signalon line 112 may, for example, be representative of the envelope of theRF signal to be amplified. As such, this reference signal gives anindication as to the instantaneous voltage level which the poweramplifier stage 108 must process, and therefore the instantaneous powersupply level which should be supplied by the voltage supply stage 104.In a highly efficient, high accuracy tracking (HAT) power supply stage,the voltage supply stage 104 tracks the reference signal in a very closemanner, such that the supply voltage provided to the power amplifierstage 108 very closely tracks the reference signal and thus ensures anefficient operation. An efficient operation is ensured by generating thenecessary supply voltage to amplify the signal to the desired level,whilst ensuring that the instantaneous supply voltage is not excessivelyabove the desired level.

As mentioned in the background section above, due to timing alignmentissues it is not generally possible in prior art arrangements to providesuch a fast envelope tracking voltage supply stage for more than oneamplifier stage of a multi-stage arrangement, particularly a widebandarrangement. Thus the driver stage 106 is provided with its own voltagesupply stage 102, which relative to the voltage supply stage 104 is aslow supply stage. Thus the voltage supply stage 102 does not providethe fast envelope tracking of the voltage supply stage 104. The voltagesupply stage 102 can adapt only slowly to changing signal conditions asrepresented by the reference signal on line 112.

In a practical implementation the voltage supply stage 104 may beimplemented as a high accuracy tracking modulated voltage supply such asdisclosed in European Patent No. 1597821. Such a voltage supply stagemay incorporate a switched supply or voltage selection stage, followedby a modulator stage. The voltage supply stage 102 may be implemented,for example, as a switched supply stage.

In a preferred arrangement, the voltage supply stage 104 may be adaptedto track instantaneous power, and deliver an appropriate supply voltageto the power amplifier stage 108; and the voltage supply stage 102 maybe adapted to track average power, and deliver an appropriate powersupply voltage to the driver stage 106. In general, the voltage supplystage 104 adapts more quickly than the voltage supply stage 102 tochanging input signal conditions. The voltage supply stage 102 may beconsidered a slow stage, and the voltage supply stage 104 may beconsidered a fast stage.

In a general form, the invention may provide an arrangement in which arelatively slow and/or relatively inefficient first tracking voltagesupply stage delivers a supply voltage to a first amplifier stage and asecond relatively fast and/or relatively efficient second trackingvoltage supply stage delivers a supply voltage to a second amplifierstage. Preferably the first supply stage delivers a power supply voltagein dependence on an average power requirement, and the second supplystage delivers a power supply voltage in dependence on an instantaneouspower requirement.

Reference to ‘average power’ is to the average power of the transmittedsignal. Thus average power information may be obtained in a number ofways, examples of which are described herein, as one skilled in the artwill appreciate. Averaging is performed over an appropriate time periodto determine the average power. Reference to ‘instantaneous power’ is tothe power, at a given time instant, in the transmitted signal. Thisinstantaneous power information may be obtained in a number of ways, asone skilled in the art will appreciate. Indeed this may be obtained byconsidering the average over a relatively short time period. The averageand instantaneous powers may be determined in dependence on the signalto be amplified.

In general herein, the voltage supply stage 102 is considered to providea power supply voltage in dependence on an average power requirement,and the voltage supply stage 108 is considered to provide a power supplyvoltage in dependence on an instantaneous power requirement. However itshould be understood that the instantaneous power requirement may bedetermined by looking at the requirement over an average period, but ashort average period. In general, therefore, the voltage supplies shouldbe considered relative to each other. The tracking of the stage 102 isslower than that of the stage 104. The voltage generated by the stage104 is dependent upon a capture of information over a smaller timeperiod than that of stage 102. ‘Instantaneous’ may be considered asaveraged over a relatively short time period.

With reference to FIGS. 2 to 5, there is now discussed four embodimentsfor implementing a multi-stage amplifier architecture in accordance withthe principles of an inventive arrangement as exemplified by FIG. 1.

With reference to FIGS. 2 to 5, it should be noted that any elementshown in the figures which correspond to elements shown in previousfigures are denoted by similar reference numerals.

The multi-stage amplifier arrangement in FIG. 2 is generally denoted byreference numeral 200, and includes the driver stage 106 and the poweramplifier stage 108. The voltage supply stage 104 of FIG. 1 isimplemented as a high accuracy tracking (HAT) voltage supply stage 206.The voltage supply stage 102 of FIG. 1 is implemented as a voltageselection stage 204 and a voltage selection control stage 202. The HATvoltage supply stage 206 is representative of a fast tracking, modulatedvoltage supply. The invention is not limited to any specific arrangementof such a supply. In general, in the illustrated embodiment, the HATvoltage supply 206 comprises a multi-supply stage 210, and a modulator208. The multi-supply stage 210, being a switched supply stage, operatesin dependence upon a reference signal, provided on a line 112 (or ingeneral as one of a plurality of control signals 228), to select one ofa plurality of fixed supply voltages at its output. The modulatoroperates as an error correction stage which receives one or morevoltages from the multi-supply stage 210, and generates thehigh-accuracy instantaneous tracking voltage. In general, the switchedsupply stage provides a supply voltage representative of an averagepower requirement of a signal to be amplified. In general the modulator,or error correction stage, corrects the switched supply to provide asupply voltage representative of an instantaneous power requirement ofthe signal to be amplified.

The control signals 228 may further include, for example, configurationand clock information.

The fixed supply voltages are generated from a battery voltage providedby a battery 212 on line 230. The battery voltage on line 230 forms aninput to the multi-supply stage 210. In the illustrated example, themulti-supply stage 210 provides four fixed output voltage levels. Thefour fixed output voltages are provided on separate lines to themodulator 208. The modulator 208 acts on one of the selected supplyvoltages, in dependence on the reference signal on line 112, to providea fast envelope tracking of the reference signal, to deliver anefficient supply voltage on line 240 to the power amplifier 108. Theoperation of such an efficient modulated power supply stage will bewell-known to one skilled in the art.

In this embodiment, the voltage selection stage 204 receives each of thevoltage levels output by the multi-supply stage 210, on respective lines222 a to 222 d. The voltage selection stage 204 selects one of thevoltage levels on lines 222 a to 222 d to provide the voltage level online 220 for the supply voltage for the driver stage 106. The selectionis made in dependence upon a control or selection signal provided online 224, which control signal is generated by the voltage selectioncontrol stage 202. The voltage selection control stage 202 generates thecontrol signal on line 224 in dependence upon control signals receivedon lines 226.

The voltage selected from the multi-supply stage 210 for each of themodulator 208 and the switcher 204 may be different.

The control signals on lines 226 preferably include the uplink transmitpower, which is determined by the network, to control the supply voltageselected in the voltage selection stage 204.

The voltage selection control stage 202 may be implemented as a look-uptable. The look-up table may be arranged to store a mapping from a powercontrol level—such as of the uplink transmit power—to a driver supplyvoltage. The table values may be chosen during the design anddevelopment phase. Alternatively the table values may be set-up during acalibration process.

As discussed above, the power supply stage 206 provides instantaneoustracking of a reference signal to provide an efficient instantaneouspower supply voltage for the power amplifier stage 108. The voltageselection stage 204, in combination with a voltage selection controlstage 202, provides an approximate power supply voltage, by selectingone of a plurality of available fixed supply voltages.

The available switched supply voltages are selected by the voltageselection control stage 202 to ensure that the driver stage can providesufficient peak RF drive power for the output stage. In a time divisionsystem, where time slots are used, such as a mobile communicationsystem, this may be updated on a time slot-by-time slot basis. For eachtime slot, an appropriate fixed voltage level is chosen. The RF powerhead room in the driver stage can then be carefully controlled so itoperates with the best possible efficiency, given the non-modulatedpower control level dependent supply.

In mobile telecommunication systems, a handset or in general a mobiledevice has a power control level (PCL) set, which determines thetransmit power of the device. This PCL may be set by the network.

The network may tell the handset which PCL should be used in a giventimeslot. This information may be conveyed by the network issuing aspecific PCL to the handset. In an alternative, such as in 3G WCDMAnetworks, the network may issue commands to the handset rather thanvalues, e.g. commands for the power level to be increased, decreased, orremain the same. This information or command may be included in thecontrol signals on lines 226.

The supply voltage levels associated with PCL levels in the look-uptable are determined taking into account appropriate factors. A PCLtypically represents the average power in a timeslot (ignoring anyramping at the start and end of the time slot). In some applications,the average and peak power may be the same, whilst in others the peakpower will be higher than the average. As the power supply selectedneeds to be sufficient for handling peak powers, the look-up table isarranged to select appropriate power levels in dependence upon a PCLlevel, taking into account these factors.

In a preferred arrangement, a clean-up block is provided on line 220,preferably with regulation, for cleaning up the supply signal beforedelivery to the amplifier.

With reference to FIG. 3, there is illustrated a second embodiment inaccordance with an inventive arrangement. The multi-stage amplifierarrangement of FIG. 3 is generally denoted by reference numeral 300, andcorresponds to that of FIG. 2 but the voltage selection stage 204 ofFIG. 2 is replaced by a multi-supply stage 302. The multi-supply stage302 is an exemplary implementation of the slow supply stage 102 of FIG.1

The multi-supply stage 302 receives the voltage signal on line 230 fromthe battery 212, and in addition receives the control or selectionsignal on line 224 from the voltage selection control stage 202. Theoutput of the multi-supply stage 302 is provided on line 304, andprovides a supply voltage for the driver stage 106.

The arrangement of FIG. 3 differs to that of FIG. 2, insofar as thepower supply stage for the driver stage is provided with its ownmulti-supply stage 302. Thus the voltage supply on line 304 provided bythe multi-supply stage is one of a multiple of available fixed supplyvoltages, generated from the battery voltage on line 230, and selectedin dependence on the control or selection signal on line 224.

A third embodiment of a multi-supply stage arrangement in accordancewith the inventive arrangement of FIG. 1 is illustrated with referenceto FIG. 4, and denoted by reference numeral 400. The arrangement of FIG.4 corresponds to that of FIG. 3, but the multi-supply stage 302 isadapted to receive a reference signal on line 410 which is derived fromthe output of the HAT 206. Thus the voltage selection control stage 202of FIG. 3 is dispensed with, and a reference signal on line 410 is usedto control the voltage of the multi-supply stage 302 to be provided as asupply voltage on line 304. The multi-supply stage can provide one of aset of fixed voltage levels as the supply voltage on line 304, orprovide a continuously varying supply voltage.

A low pass filter (LPF) denoted by reference numeral 402 receives themodulated supply voltage on line 240 delivered to the power amplifierstage, and provides a filtered version of such on line 410 as thereference signal. The low pass filter 402 thus provides on line 410 asignal corresponding to the average of the modulated power supplyvoltage generated on line 240.

The arrangement of FIG. 4 is advantageous in avoiding the need for thevoltage selection control stage 202 which provides an interface for thePCL. Thus the hardware and software complexity of the multi-stageamplifier arrangement is reduced. The arrangement allows the voltagesupply generation for each stage of the multi-stage amplifierarrangement to be self-contained.

The arrangement of FIG. 4 generates the voltage supply in dependence onan average power requirement, by deriving the average power requirementfrom the voltage supply generated in dependence on the instantaneouspower requirement. Thus the voltage supply is generated by determiningthe average of the instantaneous voltage supply.

A further modification may be made to the arrangement of FIG. 4, and anyarrangement in which the supply voltage to the driver stage is deriveddirectly from the supply voltage to the output amplifier stage. Theremay be a requirement for the voltage applied to the driver amplifierstage to be further adjusted in dependence on the peak-to-average (PAR)of the transmitted RF signal. For this purpose a scaling means (notshown) may be provided before or after the low pass filter 402. If thetransmitter is required to handle a variety of transmission formats,with varying PAR values, then PAR-dependent scaling may be appropriate.With reference to FIG. 4, the scaling means would preferably be placedsomewhere along the path between the output amplifier stage voltagesupply output and the input to the driver amplifier stage voltage supplystage. In the arrangement of FIG. 4 this requires the scaling means tobe placed before or after (i.e. at the input or output of) the low passfilter 402.

With reference to FIG. 5, there is further illustrated a fourthembodiment for implementing the multi-amplifier arrangement inaccordance with the inventive arrangement of FIG. 1. In FIG. 5, themulti-stage amplifier arrangement is generally denoted by referencenumeral 500.

The embodiment of FIG. 5 generally corresponds to that of FIG. 4, withthe addition of a sample-and-hold (SAH) block between the low passfilter 402 and the multi-supply stage 302. The output of the low passfilter 402 on a line 504 forms an input to the SAH block 502, and in theoutput of the

SAH block on line 506 forms the input to the multi-supply stage 302,being the reference signal for selection of the appropriate fixed supplyvoltage.

The sample-and-hold block ensures that the power supply stage for thedriver amplifier is provided with a reference signal, on line 506, whichremains constant across a given time slot or other given time period.The sample-and-hold block 502 may be triggered at a time slot boundary.This ensures that the supply voltage on line 304 for the driver stageremains constant for a given time slot.

The inventive arrangement is not limited to the specifics of any of thefour embodiments described hereinabove. For example, the invention isnot limited to the implementation of the power amplifier stage 108 as asingle amplifier stage. The power amplifier stage 108 may be implementedas a plurality of parallel amplifier stages. The plurality of amplifierstages may be identical, being provided for ensuring an appropriatepower level can be generated at the output thereof. Alternatively onesof the parallel power amplifier stages may be associated with differentfrequencies, such that the output amplifier stage can switch betweenones of the parallel power amplifiers according to the frequency of thesignal to be amplified.

A further inventive arrangement, which may be used in combination withor independently of the arrangements shown in each of FIGS. 1 to 5, isnow illustrated with reference to FIGS. 6 and 7. In some power amplifierarrangements, it is known to provide a bypass arrangement which allowsthe power amplifier to be bypassed when high powers are not required.Thus when a high powered signal is required to be generated, the signalis amplified by the output power amplifier, and when a low or mediumpower signal is required, the power amplifier is bypassed and not used.In a multi-stage amplifier arrangement, when the power amplifier isbypassed the signal may be amplified by only the driver stage.

When the output power amplifier is bypassed and therefore effectivelydisabled, the power supply generation for the power amplifier stage isnot needed. Thus any control provided for the generation of an efficienttracking power supply for the output amplifier is no longer required.

In accordance with this further inventive arrangement, the efficienciesachieved by the provision of a fast, modulated power supply stage arepreferably utilised when the amplifier stage for which it is provided isdisabled or bypassed.

In the foregoing, there has been described various techniques in whichan average tracking power supply may be generated for providing a powersupply to a first amplifier stage, such as amplifier 106. Otherarrangements may be used. For example, the average tracking power supplymay be derived by filtering the output of the modulator 208, andproviding the filtered signal as the supply voltage to the amplifier106.

With reference to FIG. 6, there is illustrated a multi-stage amplifierarrangement 600 similar to that of FIG. 1. The arrangement of FIG. 6differs to that of FIG. 1 in that the voltage supply stage for thedriver amplifier stage 106 is provided as a fixed voltage supply ratherthan a slowly varying (e.g. switched) voltage supply. In addition fourswitches identified by reference numeral 602, 604, 606 and 605 areprovided.

The multi-stage amplifier arrangement 600 of FIG. 6 is implemented witha fixed voltage supply stage 620 for the driver amplifier stage forpurposes of illustration. The principles discussed hereinabove withreference to each of FIGS. 1 to 5 are not essential to the inventivearrangement of FIG. 6. In an alternative, the fixed voltage supply stage620 of FIG. 6 may be implemented as a slow (or inefficient) voltagesupply stage such as supply stage 102 of FIG. 1. However, asillustrated, the voltage supply stage 620 may be a switched supply,being switched in dependence on the reference signal on line 112.

The inventive arrangement described with reference to FIG. 6 takesadvantage of the fact that the fast or efficient voltage supply stage104 is not used when the output amplifier 108 is bypassed. Therefore thearrangement is adapted such that when the output amplifier is bypassed,the fast, efficient voltage supply stage 104 is arranged to provide thevoltage supply to the driver stage 106. This is achieved by theoperation of the switches 602, 604, 605 and 606.

It should be noted that in FIG. 6 the control signals necessary tocontrol the switches are not illustrated. One skilled in the art willappreciate that such control signals are generated in order to enablethe bypassing of the output amplifier 108 in accordance with prior arttechniques. These control signals are then extended to be further usedin order to enable the inventive principles.

As illustrated in FIG. 6, each of the switches 602, 604, 605 and 606 isswitchable between two positions A and B. In the first mode ofoperation, when the output amplifier 108 is not bypassed, each switch isconnected to switch position A. In such an arrangement, the fast,efficient voltage supply stage 104 provides the supply voltage for theoutput amplifier 108, and the fixed voltage supply stage 620 providesthe voltage supply for the driver stage 106. The output of the driverstage 106 is amplified by the output amplifier 108 and the amplifiedoutput provided at its output.

It will be understood by one skilled in the art that the arrangement ofFIG. 6 is exemplary. The switching between modes may be achieved indifferent ways than those illustrated. For example, the switch 604 maybe dispensed with and the supply voltage from supply 104 connected toterminals A and B simultaneously. An alternative switch may then beprovided to bias the amplifier 108 ‘off’ in bypass mode.

In a second mode of operation, the output amplifier 108 is bypassed. Thedecision to bypass the output amplifier is taken by control circuitrywhich is not described herein. The bypassing of output amplifiers incertain conditions is known in the art, and one skilled in the art willappreciate the implementation of such control. In response to a controlsignal to bypass the output amplifier, each of the switches 602, 604,605 and 606 are switched to positions B. Thus the output of the driveramplifier 106 provides the output of the amplification stage 600, byvirtue of bypass switches 605 and 606 being switched to positions B.

In addition, the voltage supply input to the driver stage 106 isdisconnected from the fixed voltage supply stage 620, by switching ofthe switch 602 to position B. The output of the voltage supply stage 104is switched to switch position B of switch 604, such that the output ofthe voltage supply stage 104 provides the supply voltage to the driverstage 106. Thus when the output amplifier 108 is bypassed, the fast,efficient voltage supply stage 104 provides the voltage for the driverstage 106, which operates in a highly efficient manner.

Whilst the principles of this inventive arrangement are not limited tothe specifics of any of the embodiments described with reference toFIGS. 1 to 5, one skilled in the art will appreciate that the principlesmay nevertheless be extended to, and incorporated in, each of theembodiments of FIGS. 1 to 5. In order to illustrate this, FIG. 7 showsthe principles of the inventive arrangement of FIG. 6 implemented in theembodiment of FIG. 5 described hereinabove.

With reference to FIG. 7, the arrangement of FIG. 5 is adapted toinclude the plurality of switches 602, 604, 605 and 606, in amulti-stage amplifier arrangement denoted by reference numeral 700.

As described hereinabove with reference to FIG. 6, in a first mode ofoperation the output amplifier 108 is enabled for amplifying the outputof the driver stage 106. Thus each of the switches 602, 604, 605 and 606has its switch connected to terminal A, and the arrangement of FIG. 7then corresponds identically to that of FIG. 5 hereinabove.

In the second mode of operation, when a control signal indicates thatthe output amplifier 108 should be bypassed, each of the switches 602,604, 605 and 606 is controlled to connect to terminal B. In this way,and as described hereinabove with reference to FIG. 6, the outputamplifier 106 is bypassed, and the output of the driver stage providesthe output of the multi-stage amplifier 700. In addition, the output ofthe fast, modulated supply stage 206 provides the voltage supply for thedriver stage 106 via switches 604 and 602, such that the driver stage106 operates in a highly efficient manner.

With reference to FIG. 8, a further example arrangement in accordancewith one or more inventive or preferable arrangements is described.These arrangements are described in accordance with the principles ofFIGS. 6 and 7. In particular the arrangement of FIG. 8 is presented as amodification to the arrangement of FIG. 7. It is not, however, limitedto the specifics of the arrangement of FIG. 7.

However none of the specific features shown in FIG. 8 or described inthe context of FIG. 8 are limited to being dependent upon any particularcombination of features with which they are described or which aredescribed elsewhere in this description. Any individual featuredescribed herein may be implemented on its own or in combination withone or more described features.

With reference to the example arrangement of FIG. 8, the multi-supplystage 302 of FIG. 7 is illustrated as providing a supply voltage for theamplifier 106 via a switch 705. This is for ease of illustration only.Alternatively a supply voltage may be supplied to the amplifier 106 fromthe switched supply output of the multi-stage supply 210, also viaswitch 705, on line 706. A switch 704 is provided to select one of thesupply voltages at the output of the multi-stage supply 210, and providethat on a line 706. In such an arrangement a clean-up block, preferablywith regulation, may be provided on line 706.

The provision of the supply voltage may be provided to the amplifier 106in accordance with any technique described herein. Both optionsillustrated in FIG. 8 deliver a tracked average supply voltage to theamplifier 106. An alternative averaged supply voltage may be provided byfiltering the instantaneous tracked voltage on line 708 and providingthat as the supply voltage for the amplifier 106.

In addition, in certain modes of operation, and in particular where theoutput amplifier stage is bypassed, the instantaneous tracked supplyvoltage may be provided to the supply terminal of the amplifier 106.

The tracked instantaneous supply voltage from the modulator 208 isprovided on line 708.

A switch 702 is provided to select between the signals on lines 706 and708, and connect one to a supply line 710. The supply line 720 connectsthe selected supply to the supply terminals of two amplifiers: theamplifier 108 and an amplifier 707.

The amplifiers 108 and 707 are preferably—in one arrangement—foramplifying different magnitudes or ranges of signals. In such anexemplary arrangement the circuit is controlled such that one amplifieris connected to amplify signals at any one time. In dependence uponwhich amplifier is enabled, either the average (slow) supply voltage online 706 or the instantaneous (fast) supply voltage on line 708 isprovided.

Thus, for example, in the event that the amplifier 108 is needed toamplify the signals, in an arrangement all switches 605, 606 and 702 areswitched to positions A. In the event that the amplifier 708 is neededto amplify the signals, all switches 605, 606 and 702 are switched topositions B.

Alternative arrangements are envisaged. In the example above, theamplifier 106 receives a tracked average supply voltage. In general, theamplifier 106 may receive a tracked average supply voltage in a numberof different ways, from different sources. In such arrangements thesupply voltage to the amplifier 106 may be switched so as it may beconnected to more than one source, or may be fixed to one source.

In a mode of operation in which a subsequent amplifier stage isbypassed, the amplifier 106 may receive a tracked instantaneous supplyvoltage. In such arrangements the supply voltage to the amplifier 106may be switched so as it may be connected to more the source of eitherthe average or instantaneous tracked supply.

The amplifier stage, as represented by amplifiers 108 and 707 in FIG. 8,may in general comprise n amplifiers. The amplifiers may be arrangedsuch that any one of the n amplifiers may be selected or a sub-set ofthe n amplifiers may be selected. When a plurality of amplifiers areselected, each of the selected amplifiers is connected to the samesupply voltage. The supply voltage may be a tracked instantaneous supplyvoltage or a tracked average supply voltage. The source of trackedinstantaneous supply voltage or the tracked average supply voltage maybe any source described in this description.

In an arrangement where more than one parallel amplifier, such asamplifiers 108 and 707, are selected or enabled at the same time, suchan arrangement may be a Doherty arrangement. However two or moreparallel amplifiers may be selected or enabled at the same time in anon-Doherty configuration.

Each of the amplifiers 108 and 707 may be enabled/disabled or selectedas described herein, with either the amplifier 108 or amplifier 707comprising an amplifier stage consisting of a plurality of amplifiers,which respective plurality of amplifiers comprise a set which areenabled/disabled together.

Various other modifications are possible.

In general a power amplifier stage may have two or more amplifiersconnected in parallel. In one operating mode, typically at high powerRF, an envelope tracking scheme is preferably used to deliver a supplyvoltage to the power amplifier stage. In another mode, the poweramplifier stage preferably receives a power-level dependent supply.

Whilst in one mode of operation two or more stages of the parallel poweramplifier stage are used for amplifying different magnitudes ranges ofsignals, and only one is enabled at a time, in alternative arrangements,such as a Doherty arrangement or similar arrangement operating at highpower, for example, two or more amplifiers may operate simultaneously.

Where an amplifier is disabled or ‘switched off’ in any mode ofoperation, this may be achieved by any suitable mechanism. For example adisabled amplifier may be biased ‘off’ of switched out of the circuit.The power supply to a disabled amplifier may be switched off, and thuseach individual amplifier may have an individual switch for switching toa supply voltage, to allow such switching to take place.

It should be understood that various aspects of each of the inventivearrangements and embodiments described herein may be implemented inisolation or in combination. Thus a feature disclosed in any embodimentherein may be combined with a feature of another embodiment. Featuresillustrated in one embodiment are not essential for the implementationof other features in other embodiments.

The invention has been described herein by way of particularembodiments, which are useful for understanding the invention and itspreferred implementations. The invention is not, however, limited to thespecifics of any implementation. The scope of the invention is definedin the appended claims.

1-52. (canceled)
 53. A multi-stage amplifier comprising: a driveramplifier stage; a power amplifier stage; a switched mode supply stagearranged to provide a supply voltage to the driver amplifier independence on an average power of a signal to be amplified; and anenvelope tracking modulated power supply stage arranged to provide asupply voltage to the power amplifier in dependence on an instantaneouspower of a signal to be amplified, wherein the envelope trackingmodulated power supply stage tracks the envelope of a signal to beamplified faster than the switched supply stage.
 54. The multi-stageamplifier of claim 53 wherein the switched supply stage selects one of aplurality of supply voltages generated in the envelope trackingmodulated power supply stage.
 55. The multi-stage amplifier of claim 53further comprising means for determining the instantaneous power and theaverage power, wherein the average power is determined over apredetermined time interval.
 56. The multi-stage amplifier of claim 53wherein there is provided a means for determining the average of thesupply generated by the envelope tracking modulated power supply stage,and providing the switched supply voltage in dependence upon thedetermined average.
 57. The multi-stage amplifier of claim 56 whereinthe means for determining the average of the supply generated by theenvelope tracking modulated power supply stage comprises a low passfilter.
 58. The multi-stage amplifier of claim 56 wherein the switchedsupply stage is controlled by the determined average.
 59. Themulti-stage amplifier of claim 56, further comprising a sample-and-holdstage for sampling the determined average.
 60. The multi-stage amplifierof claim 53, wherein the switched and envelope tracking modulated powersupply stages are arranged to selectively provide supply voltages to thedriver and power amplifier stages, wherein in a first mode of operationa signal is amplified by the driver and power amplifier stages, and theswitched supply voltage stage is selected to provide a supply voltage tothe driver amplifier stage and the envelope tracking modulated powersupply stage is selected to provide a supply voltage to the poweramplifier stage, and in a second mode of operation the power amplifieris bypassed, the signal being amplified by the driver amplifier stage,and the envelope tracking modulated power supply stage being selected toprovide a supply voltage to the driver amplifier stage.
 61. A method ofamplifying a signal in an amplification stage comprising a driveramplifier stage; a power amplifier stage; a switched mode voltage supplystage; and an envelope tracking modulated power supply stage, the methodcomprising: arranging the switched voltage supply stage to provide asupply voltage to the driver amplifier in dependence on an average powerof a signal to be amplified; and arranging the envelope trackingmodulated power supply stage to provide a supply voltage to the poweramplifier in dependence on an instantaneous power of the signal to beamplified, wherein the envelope tracking modulated power supply tracksthe envelope of a signal to be amplified faster than the switched supplystage.
 62. The method of claim 61 wherein the switched supply stageselects one of a plurality of supply voltages generated in the envelopetracking modulated power supply stage.
 63. The method of claim 61further comprising determining the average of the supply generated bythe envelope tracking modulated power supply stage, and providing theswitched supply voltage in dependence upon the determined average. 64.The method of claim 63 wherein the step of determining the average ofthe supply generated by the envelope tracking modulated power supplystage comprises low pass filtering.
 65. The method of claim 63 whereinthe switched voltage supply stage is controlled by the determinedaverage.
 66. The method of claim 63 further comprising sampling thedetermined average.
 67. The method of claim 61, wherein the switched andenvelope tracking modulated power supply stages selectively providesupply voltages to the driver and power amplifier stages, wherein in afirst mode of operation a signal is amplified by the driver and poweramplifier stages, and the switched supply voltage stage is selected toprovide a supply voltage to the driver amplifier stage and the envelopetracking modulated power supply stage is selected to provide a supplyvoltage to the power amplifier stage, and in a second mode of operationthe power amplifier is bypassed, the signal being amplified by thedriver amplifier stage, and the envelope tracking modulated power supplystage is selected to provide a supply voltage to the first amplifierstage.